Geologic resources and economic geology

Physical Geology Lecture

Lecture outline: Introduction, Metallic Ore Deposits, Energy Resources, Groundwater


Introduction

What is the most important or valuable resource that geologists look for? For many gold, oil and diamonds may spring to mind. The geology of each of these types of deposits is fascinating, but arguably our most important resource is groundwater. However, there is no need to stop there in considering geologic resources. In addition, geologists are involved in finding and assessing deposits of a whole assortment of other valuable resources, including clays and limestone to make cement. The various industrial uses of clay may surprise one. With the advent of new technology, rare earth elements have become more sought after. Geologic resources are not spread evenly over the surface of the unit, and this simple fact has many significant political implications.

View of gold ore from Nevada deposit. Image source: http://minerals.usgs.gov/west/projects/nngd.htm

What are major groups of geologic resources? Answer.


Metallic Ore Deposits

Homestake Gold Mine in the Black Hills of South Dakota. The surface pit started in the 1870s, and underground mining extended 6800' deep. Mining operations are now closed, and at depth is the site of a neutrino laboratory..

A view of ore deposits as a geologic anomaly:

What are the geologic concentration processes that produce ore anomalies? Answer.


Energy resources

What are the various types of geologic energy resources? Answer.

What are the geologic requirements for formation of oil and gas deposits? Answer.

How do we explore for oil and gas? Answer.

Right: Photograph of oil drilling rig in Oklahoma in 1981, during the oil crunch, when exploration in the U.S. was vigorous.

"Fracking" technology, which changed the basic picture of fossil fuel energy reserves for the U.S. and the world, consists of 4 components:

Significant waste water volume is produced during the oil and gas production, and is typically reinjected at disposal wells. It is with these disposal wells that earthquakes are associated. The associated physics are well understood.

Diagram showing many of the critical aspects of fracking operations. The horizontal well section can go along a geologic reservoir for a mile or so. Image source: USGS site, Water Quality Topics: Hydraulic Fracking - http://water.usgs.gov/owq/topics/hydraulic-fracturing/ .

Conditions of formation of coal?

Image of location of peat accumulation in California. This is part of a wetland reconstruction and carbon sequestration project by the USGS - http://ca.water.usgs.gov/news/release070809.html

USGS photo of coal strip mine in Powder River Basin of Wyoming.

Cradle to grave perspective on coal: If one considers the whole suite of costs and benefits from exploration, to extraction, to processing, to use, to waste disposal what does the picture look like?

Uranium as an energy mineral:

Crow Butte deposit near Crawford in northwest Nebraska:

Environmental considerations associated with nuclear power are significant:

Geopolitical considerations are significant:

A bit more on nuclear power: http://maps.unomaha.edu/maher/GEOL1010/lecture21/lecture21.html


Ground water

This is the science of geohydrology.

How much water can the ground hold? Answer.

What are the physics of fluid flow through rocks? Answer.

How does groundwater connect to the rest of the hydrologic cycle? Answer.

Examples of aquifers.

Usually aquifers are subsurface features and hard to see, but if you learn what to look for some aquifers can have manifestations at the surface. In this image from the Niobrara River valley east of Valentine Nebraska two features are of groundwater significance: the line of trees growing midway in the cliff section here, and the staining by water of the lower section. The upper stratigraphic unit here, above the tree line is part of the Ogallala Group (and aquifer), and the lower portion is the clay rich Rosebud Formation. The Rosebud Formation acts as the impermeable floor to the aquifer (because it is clay rich), and the staining is groundwater leaking out of the overlying aquifer as seeps, and the constant source of water helps the vegetation take a hold, albeit a precarious one. In this way one can also see how the aquifer is linked to the river.

Some information and maps (make sure you check out the maps) associated with the Ogallala (High Plains) aquifer - USGS site: http://ne.water.usgs.gov/ogw/hpwlms/hydsett.html .

Image of simplified model for coastal aquifers where a "bubble" of less dense fresh water sits on top of denser seawater. Mixing is limited because the water is moving through pore space where turbulent mixing can't occur. This is one reason that freshwater springs can occur along coast lines. Image source: USGS website - http://water.usgs.gov/ogw/gwrp/saltwater/salt.html .

We deal with this topic in a lot more detail in GEOL 1010, Environmental Geology.

Dowsing and water witching.


© Harmon D. Maher Jr. This page may be reproduced for non-profit educational purposes with source acknowledgement. Otherwise please contact me. Thank you.

Return to Physical Geology index page.

Return to my home page index.